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| United States Patent |
6,146,760
|
|
Helfer
, et al.
|
November 14, 2000
|
High strength cord
Abstract
Steel reinforcing cords (36) having four or more filaments (38, 40, 42 and
44) in two groups, one twisted and the other untwisted with a filament
tensile strength TS equal to K.sub.1 -K.sub.2 D where K.sub.1
=4080N/mm.sup.2, and D is a filament diameter in mm to form cords with a
break load equal to N(720.40D.sup.2 -352.6D.sup.3 ; CE is the cord
efficiency, D is the filament diameter in millimeters and N is the number
of filaments.
| Inventors:
|
Helfer; Farrel Bruce (Akron, OH);
Kim; Dong Kwang (Akron, OH);
Shemenski; Robert Martin (North Canton, OH);
Sinopoli; Italo Marziale (Canton, OH);
Jeanpierre; Guy (Bissen, LU);
Nguyen; Gia Van (Arlon, BE)
|
| Assignee:
|
The Goodyear Tire & Rubber Company (Akron, OH)
|
| Appl. No.:
|
879860 |
| Filed:
|
June 20, 1997 |
| Current U.S. Class: |
428/377; 57/212; 57/217; 57/218; 57/243; 57/902; 428/295.1; 428/379; 428/390 |
| Intern'l Class: |
D02G 003/36 |
| Field of Search: |
428/377,295.1,379,390
57/212,217,218,243,902
|
References Cited
U.S. Patent Documents
| 4408444 | Oct., 1983 | Baillievier | 57/237.
|
| 4506500 | Mar., 1985 | Myauchi et al. | 57/212.
|
| 4516395 | May., 1985 | Palmer et al. | 57/237.
|
| 4545190 | Oct., 1985 | Rye et al. | 57/212.
|
| 4737392 | Apr., 1988 | Dambre | 428/36.
|
| 4960473 | Oct., 1990 | Kim et al. | 148/12.
|
| 4966216 | Oct., 1990 | Kawasaki et al. | 152/556.
|
| Foreign Patent Documents |
| 0076882 | Apr., 1991 | JP.
| |
| 93195455 | Aug., 1993 | JP.
| |
Primary Examiner: Raimund; Christopher
Attorney, Agent or Firm: Lewandowski; T P
Parent Case Text
This is a continuation of application(s) Ser. No. 07/843,133, filed on Feb.
28, 1992; now abandoned, which is a continuation of Ser. No. 07/575,027
filed Aug. 30, 1990, now abandoned, which is a CIP of U.S. application
Ser. No. 07/496,759 filed Mar. 21, 1990, now U.S. Pat. No. H001,333, and
with assignee's U.S. application Ser. No. 07/415948 filed Oct. 2, 1989,
now U.S. Pat. No. 4,960,473 which discloses steel alloys for reinforcing
wires/filaments for rubber products with increased strength and ductility
and their process of manufacture which is hereby incorporated by reference
thereto.
Claims
We claim:
1. A cord of the U+T type for reinforcing elastomeric structures with two
groups of filaments in the cord, group T being twisted and group U
untwisted with the two groups twisted about each other comprising: at
least two filaments in each group, all filaments having the same pitch and
twist direction, said cord made of steel having a cord breaking load (CBL)
in pounds defined by the expression: CBL=N(720.4D.sup.2 -325.6D.sup.3)CE
where CE is cord efficiency in a range of 0.95 to 0.99, D is the filament
diameter in millimeters in a range of 0.30 to 0.39 and N is the number of
filaments in the cord, said steel for the cord having a composition by
weight of between 0.78% and 0.86% to carbon, 0.3% and 1.0% Si and between
0.1% and 0.5% of an alloying element selected from the group consisting
of: Cr, Ni, Co, W, Mo, V, N6, and any combination thereof with, the
balance of the cord position being iron and residuals.
2. The cord in claim 1 wherein one group has three (3) filaments and N=5.
3. The cord in claim 1 wherein both groups have three (3) filaments and
N=6.
4. The cord in claim 1, 2 or 3 where CE is 0.97.
5. The cord in claim 1, 2, or 3 where D is 0.35.
Description
The present invention relates to cord and cord reinforced plies.
Particularly, the present invention relates to a cord reinforced composite
having rubber where preferably the structure is for reinforcing tires.
Reinforced elastomeric articles are well known in the art for example for
conveyor or like type belts, tires etc. Cords made of multi twisted
filaments of fine wire with two or more filaments in a single strand
construction having a wrap filament therearound to reinforce the above
structure have also been known. More recently multi strand and multi-layer
cords such as 2+7x.22+1 have been found necessary to meet the higher
demand of durability for composites in tire belts but are more expensive
to make. Even more recently, there has been use of single strand cords of
multi filaments which are not twisted about each other but rather twisted
altogether as a bundle or bunch to simplify the cord construction and
multi-directional cords. Higher fatigue life requirements for composites
in tires have resulted in cords with smaller filament diameter requiring
more filaments in the cord to obtain the necessary strength.
Most recently two ply tire belts for passenger and light truck tires have
been used having cords of 2x.30HT and 2+2x.30HT, respectively. An example
of the 2x cord can be found in Assignee's prior application, now published
as EP 0 237462 on Sep. 16, 1987. These cords were made of high tensile
(HI) steel of a carbon content by weight greater than 0.80% which was of a
lesser strength than the above steel alloys which will be referred to
herein as super tensile (ST).
Many problems have had to be overcome even after development of the above
steel alloys and filaments. The higher strength steel alloys resulted in
changes in cord modulus giving rise to the possibility of adjusting the
parameters of a tire belt gross load described in the above identified 2x
cord application as depending upon three factors assuming adequate cord to
rubber adhesion. The factors are cord modulus, the ratio of cord volume to
rubber volume which is often expressed as the number of cord ends per
inch, and the angle of cord reinforcement. An increase in the
above-mentioned two other cord related factors generally results in an
increase of weight for the belt. Added weight means added cost and higher
rolling resistance of a tire. Lighter cords with a lower modulus do not
solve the problem because even though they have lower weight they also
have a lower cord modulus which must be offset by increasing the ratio of
cord to rubber volume. This increase in cord volume is limited by the
physical size of the cord and the resulting spacing between the cords
which governs the ability of the rubber to penetrate between the cords for
good cord to rubber adhesion.
The challenge was to determine cord structure which could take advantage of
the new cord modulus while not adversely affecting cord volume to rubber
volume ratio on lateral reinforcement.
After considerable study, effort, testing and time, the present invention
provided cords with a substantially reduced number of filaments. While a
reduction in the number of filaments would lead one to expect a reduction
in weight, this would not necessarily be the case where the filament size
was increased. Under such circumstances, cord was found for use by varying
the ends per inch (EPI) in the plies of the belt. Other advantages which
exist in the present invention include a reduction in the cord gum coat
gauge between the cord layers in a belt and a weight reduction due to
reduction in weight of reinforcement as well as reduction in an amount of
gum gauge. This also results in a reduction in cost for the composite of
the present invention.
As indicated below, the present invention will be shown to have
substantially maintained the gross load for a tire belt while reducing
weight and cost using stronger filament in cord constructions not useable
previously, even with high tensile filaments, and accompanying cord
volumes and angles which reduce material in the belt. Similar advantages
can be and have been achieved with other composites such as carcass plies
as well.
A cord for a reinforced composite structure according to the present
invention is preferably made of multiple filaments having a diameter range
of 0.30 to 0.39 mm, each filament made of steel having at least a tensile
strength (TS) defined by the expression: TS=K.sub.1 -K.sub.2 D where
K.sub.1 =4080 N/mm.sup.2, K.sub.2 =2000 N/mm.sup.2 and D is the filament
diameter in mm.
Also included is a cord of the U+T type for reinforcing elastomeric
structures with two groups of filaments in the cord, group T being twisted
and group U untwisted with the two groups twisted about each other
comprising, at least three filaments all having the same pitch and twist
direction, said cord made of steel having a cord breaking load (CBL) in
pounds defined by the expression: CBL=N(720.4D.sup.2 -352.6D.sup.3)CE
where CE is the cord efficiency, D is the filament diameter in millimeters
and N is the number of filaments in the cord.
Further, the above cords are of a simpler construction over predecessor
multi-layer cords, taking the form of 2+2, 3+2, 3+3 and U+T where T and U
represent the number of filaments in each group forming the cord. By
varying the filament size, cord constructions for several tire belts or
composites can be obtained.
Also included is a cord of the U+T type for reinforcing elastomeric
structures with two groups of filaments in the cord, group T being twisted
and group U untwisted with the two groups twisted about each other
comprising at least three filaments all having the same pitch and twist
direction, said cord made of steel having at least a tensile strength (TS)
defined by the expression: TS=K.sub.1 -K.sub.2 D where K.sub.1 =4080
N/mm.sup.2, K.sub.2 =2000 N/mm.sup.3 and D is the filament diameter in mm.
Further included is a cord of the U+T type for reinforcing elastomeric
structures with two groups of filaments in the cord, group T being twisted
and group U untwisted with the two groups twisted about each other
comprising at least three filaments all having the same pitch and twist
direction, said cord made of steel having a content by weight of between
0.78% and 0.86% carbon, 0.3% and 1.0% Si and between 0.1% and 0.5% of an
alloying element from a class of the following elements: Cr, Ni, Co, W,
Mo, V and Nb and any combination thereof, the balance being iron and
residuals.
The above cords have the advantages of a 7 to 9% increase in cord breaking
load over a predecessor cord of the same construction made of high tensile
steel.
Further, all of the above cords result-in lower linear density in the
reinforcement for which they are used which again results in less weight
and lower cost for the reinforcement and its product, be it tire, belt or
any other reinforced elastomeric.
The above advantages of the invention will become readily apparent to one
skilled in the art from reading the following detailed description of an
embodiment of the invention when considered in the light of the
accompanying drawings in which
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1-3 are cross sections through cords in accordance with an embodiment
of the present invention;
FIG. 4 is a schematic of a composite in accordance with the present
invention; and
FIGS. 5-13 are schematics of cross sections through a cord in accordance
with the present invention illustrating an idealized geometric shape taken
along the axial length of one twist of the cord.
As used herein and in the claims: "Carcass" means the tire structure apart
from the belt structure, tread, undertread, and sidewall rubber over the
plies, but including the beads. "Cord" means one or more of the
reinforcement elements, formed by one or more filaments/wires which may or
may not be twisted or otherwise formed which may further include strands
so formed which strands may or may not be also so formed, of which the
plies in the tire are comprised. "Super Tensile Steel" (ST) means a steel
as defined in the above referenced application Ser. No. 07/415948, or a
tensile strength of at least TS=K.sub.1 -K.sub.2 D where K.sub.1 =4080
N/mm.sup.2, K.sub.2 =2000 N/mm.sup.2 and D is the filament diameter in mm.
Steel reinforcing cords 36 according to the present invention (see FIGS.
1-3) are characterized by the cords 36 having filaments 38,40,42 and 44
with a tensile strength of at least 3380 N/mm.sup.2.
Preferably the cords 36 are comprised of four filaments of finely drawn
super tensile steel wire. As noted in the application incorporated by
reference above, there are a number of metallurgical embodiments which
result in the tensile strength defined above as super tensile (ST).
The cords 36 used in the working example have a structure of four filaments
38,40,42 and 44 of 0.35 mm diameter super tensile steel wire and a cord 36
break strength of 1258 Newtons plus or minus 70 Newtons. Each cord 36 has
two filaments 38,40 twisted together with a 16 mm lay length and these two
filaments 38,40 are twisted at a 16 mm lay length together with the
remaining two filaments 42,44 which are untwisted and parallel to each
other when twisted together with the twisted filaments 38,40 all in the
same twist direction. This cord is designated as 2+2x.35ST. The 2+2
construction is known for its openness and good rubber penetration
resulting from the openness. The 0.35 designates the filament diameter in
millimeters and the ST designates the material being super tensile.
Other cords produced included 3+2x.35ST and 3+3x.35ST.
These cords have particular application to composites for truck tires when
replacing former constructions.
By comparing the ratio of strength (STR) of the cord divided by the linear
density (LD) of the cords (STR/LD) advantages of the cords become
apparent:
TABLE 1
______________________________________
LINEAR
STRENGTH DENSITY
(N) Mg/Meters STR/LD
______________________________________
Former Cords
3 .times. .265/9 .times. .245 HT + 1
1810 +/ 100
4845 .37
3 .times. .20 + 6 .times. .35 HT
1850 +/ 107
5400 .34
3 + 9 + 15 .times. .22 + 1
2750 +/ 150
8470 .32
Present Cords
2 + 2 .times. .35 ST
1254 +/ 67 3048 .42
3 + 2 .times. .35 ST
1568 +/ 80 3773 .42
3 + 3 .times. .35 ST
1881 +/ 100
4527 .42
______________________________________
By comparing the ratio of strength to the linear density of the cords it
can be seen that the ratio is always higher for the present cords. It will
be shown below how the increased STR/LD of the above constructions can be
utilized to make composites that at equal inch strength yield lower total
weight.
For example, Former Cord 3x.265/9x.245HT+1 at an EPI of 12 (4.7 ends/cm)
and a minimum cord strength of 1708 Newtons yields a composite strength of
8071 Newtons per cm. If the gauge of calendered gum applied to the cords
is maintained the same for all cords, the following table results:
TABLE 2
______________________________________
CORD
END COUNT STRENGTH
ENDS PER CM MIN AVG
Per In N N
______________________________________
Former Cords
3 .times. .265/9 .times. .245 HT + 1
4.7 (12) 1708 1810
3 .times. .20 + 6 .times. .35 HT
4.3 (11) 1743 1846
3 + 9 + 15 .times. .22 + 1
3.1 (8) 2598 2749
Present Cords
2 + 2 .times. .35 ST
6.9 (17.5) 1188 1259
3 + 2 .times. .35 ST
5.5 (14.0) 1486 1575
3 + 3 .times. .35 ST
4.5 (11.5) 1779 1877
______________________________________
1000 in.sup.2 of Composite
WEIGHT
CORD GUM TOTAL STRENGTH
Kg Kg Kg N/CM
______________________________________
Former Cords
3 .times. .265/9 .times. .245 HT + 1
1.48 1.32 2.81 8071
3 .times. .20 + 6 .times. .35 HT
1.68 1.37 3.05 7919
3 + 9 + 15 .times. .22 + 1
1.72 1.50 3.21 8183
Present Cords
2 + 2 .times. .35 ST
1.34 1.32 2.66 8183
3 + 2 .times. .35 ST
1.34 1.38 2.72 8190
3 + 3 .times. .35 ST
1.32 1.40 2.72 8057
______________________________________
Table 2 above in the last column gives the composite strengths in Newtons
per centimeter of all composites with the noted cords and End Counts (ends
per cm) all of which are in the 8000 range and considered equal. The
Former Cords are listed first and the Present Cords, which are according
to the invention, are listed below with the Former Cords replaceable by
the Present Cords. The increase in STR/LD of the Present Cords over the
former permits flexibility in cord use making the Present Cords
interchangeable in composites with the proper end count. In each instance,
cord according to the present invention is simpler in construction having
fewer filaments. While the cord strength is less than the cord it
replaces, the EPI and additional strength of the super tensile filament
material allow the composites to have equal strength. However, the present
cords can be seen to have less weight with the results that a lighter
weight composite is obtained with equal inch strength which can contribute
to a more fuel efficient tire. Further, the above weight reduction is
amplified by an accompanying reduction in composite cost of up to 18%.
Table 3, below, gives a direct comparison between a number of 4 filament
cords of high tensile HT and super tensile ST of varying filament
diameters showing an increase in strength in al cases. The table gives
values in Newtons for the CBL formula N(720.4D.sup.2 -352.6D.sup.3) CE
given above in pounds where CE is the efficiency of the cord, i.e. the
difference between the cord break load over the value of the filament
break load times the number of filaments in the cord. The values in each
case can be measured by breaking each (cord and filament) and the
efficiency calculated using the values measured. Note that not all the
cord samples in Table 3 became candidates noted above.
TABLE 3
______________________________________
CORD STRENGTH
Strength in Newtons = Filament Break Load .times.
Number of Filaments .times. CE (.97)
HT Tensile of ST Tensile of
CORD Avg Min Avg Min
______________________________________
2 + 2 .times. .30
890 845 952 903
2 + 2 .times. .325
1032 979 1103 1050
2 + 2 .times. .35
1188 1125 1259 1188
2 + 2 .times. .38
1370 1303 1437 1388
3 + 2 .times. .35
1486 1406 1575 1486
3 + 3 .times. .35
1779 1686 1877 1779
______________________________________
Another advantage of the Present Cord over the former is that their
construction is more open to penetration by the calendered gum resulting
in their being more resistant to corrosion propagation. Table 4 below
makes a comparison of pull out force and observed gum coverage for various
cords initially and after two days of steam aging.
TABLE 4
______________________________________
ORIGINAL STEAM AGED
% %
N Coverage N Coverage
______________________________________
Former Cord
3 .times. .265/9 .times. .245 HT + 1
829 90 674 80
3 + 9 + 15 .times. .22 + 1
931 90 763 80
Present Cord
3 + 2 .times. .35 ST
739 90 749 90
2 + 2 .times. .35 ST
644 90 638 90
______________________________________
It can be seen that the Present Cords retain their pull out force and
coverage while the former cords drop in strength and coverage. Similar
results were achieved with salt and humidity aging.
The Present Cords are stronger in cord strength allowing for use of fewer
cords for equal strength. Those having larger diameter filaments result in
substantial reduction in the number of filaments in the cord over former
cords making use of U+T type constructions possible where previous
strength levels ruled out such type constructions. The U+T type
constructions are more open resulting in better adhesion and greater
resistance to corrosion. Finally, as noted above, the new cords lead to
reduction in weight of reinforcement in elastomers both from the
reinforcement itself as well as from the elastomer.
In accordance with the provisions of the patent statutes, the principle and
mode of operation of the cord have been explained and what is considered
to represent its best embodiment has been illustrated and described. It
should, however, be understood that the invention may be practiced
otherwise than as specifically illustrated and described without departing
from its spirit or scope.
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